Extended Forecast Discussion NWS Weather Prediction Center College Park MD 259 PM EST Mon Jan 31 2022 Valid 12Z Thu Feb 03 2022 - 12Z Mon Feb 07 2022 ...Heavy rainfall likely from the central Gulf Coast through Tennessee Valley on Thursday, with a significant winter storm from the Midwest to Great Lakes and interior Northeast... ...Overview... Expect a positively tilted mean trough aloft to prevail across much of the CONUS through the medium range period, as strong upper ridging builds over the eastern Pacific (periodically extending into parts of the West) while a strong western Atlantic ridge gradually weakens/moves eastward. The most confident part of the forecast involves the combination of a Rockies shortwave and northern stream flow that will drive a potent and wavy cold front through the eastern U.S. Thursday-Friday, bringing widespread heavy rain to the South and a potentially significant winter storm from the Ohio Valley to the interior Northeast. After Friday there is greater uncertainty over details of additional shortwaves dropping down the east side of the ridge in the West, and maybe energy lingering from the first shortwave, plus the influence of northern stream flow (supporting a series of northern tier waves). Details of these features and their possible interaction will determine how much precipitation may fall over parts of the East from the weekend into the start of next week. ...Guidance Evaluation/Predictability Assessment... A general blend of 00Z/06Z model guidance provided a good representation of consensus for days 3-4 Thursday-Friday, with the only adjustments from continuity being typical run-to-run detail changes. In this time frame, frontal waves over the East should consolidate into a single low that ultimately tracks away from New England while a weak wave and frontal system reach the northern tier. After Friday the past 12 hours of GFS runs have trended noticeably sharper and slower with shortwave energy coming into western North America, with the GFS continuing to be slower than consensus (including the GEFS mean) for northern stream flow through the rest of the period. This difference causes the GFS to be slower (and in the 06Z run, quite suppressed) with the next northern tier system and then to lower surface pressures more over the East with much broader coverage of precipitation. There is some agreement on low pressure developing off the East Coast by next Monday though. Meanwhile there is a general signal for incoming western U.S. energy to drop into a trough/upper low near the western half of the U.S.-Mexico border, with low confidence in details given the small scale of the potential upper low. By day 7 Monday the GEFS/ECMWF means provide a good intermediate solution for a shortwave that may approach the Pacific Northwest, weaker than the 00Z ECMWF but better defined/slower than some GFS runs. Based on these considerations, the updated forecast based on guidance through the 06Z cycle lowered GFS weight starting day 5 Saturday and increased 06Z GEFS/00Z ECMWF mean input so that models and means had equal weight by day 7 Monday. The new 12Z ECMWF provides some added intrigue, with partial trends in the GFS direction for northern stream flow while keeping weekend into Monday shortwave energy more phased (eliminating the compact closed low dropping into the Southwest). ...Weather Highlights/Threats... Amplified trough emerging from the Southwest on Thursday and leading wavy cold front will continue the threat for heavy rainfall and a significant winter storm to the north into the Thursday-Friday time period. Ample Gulf moisture streaming northward ahead of the upper trough and associated surface cold front will promote widespread moderate to heavy precipitation from the lower Mississippi Valley into the Northeast. Best chance for heavy rainfall extends from the central Gulf Coast into Ohio Valley on Thursday then extending into the southern/central Appalachians and interior East. The overall pattern continues to support a threat for excessive rainfall/flash flooding. Although plenty of uncertainties in the details linger, models seem to be gravitating toward the idea of the greatest threat being from the central Gulf Coast into the Tennessee Valley where anomalous precipitable water values, lift enhanced by favorable upper jet dynamics, and moderate instability should support several inches of rainfall across this region. On there north side of the precipitation shield, the threat for a significant winter storm into parts of the Ohio Valley/Great Lakes/interior Northeast will continue from the short range period. Heavy accumulating snow is likely, while possible impactful sleet and freezing rain just to the south within the transition zone between the rain to the south and snow to the north. Exact amounts of any wintry precipitation remain highly dependent on the lower-confidence details of ejecting shortwave energy, frontal waves, and timing of colder temperatures. Elsewhere, northern tier systems may produce a couple episodes of light and scattered snowfall. Mostly light rain/mountain snow should accompany a couple systems brushing the Pacific Northwest and possibly extending into the northern Rockies. Significant guidance differences with separate streams of energy aloft lead to low confidence in the coverage and amounts of precipitation over the South and East from the weekend into the start of next week. Some precipitation type issues may come into play depending on how far north the moisture shield extends. Areas ahead of the eastern U.S. cold front will see above average temperatures Thursday-Friday, with plus 10-15F anomalies for highs and up to plus 20-30F anomalies for morning lows. Arctic high pressure diving into the central U.S. behind the cold front will bring very cold temperatures to the Central U.S. and Midwest after midweek. On Thursday-Friday expect widespread daytime highs (and slightly less extreme overnight lows) as much as 10-25 degrees below average with values as much as 30-35 below normal over parts of Oklahoma/Texas/eastern New Mexico on Thursday. During the weekend a modified form of this cold air will reach portions of the East while the southern Plains gradually moderate but remain well below normal. Meanwhile the pattern will favor above normal temperatures over the northern Plains Saturday-Monday with some areas seeing one or more days of plus 10-20F anomalies. The West Coast states should be near normal into weekend, trending slightly warmer the rest of the period owing to amplified ridging across the East Pacific. Rausch/Santorelli Additional 3-7 Day Hazard information can be found on the WPC medium range hazards outlook chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml